DHPG or B759U are identical Acyclovir congeners which have excellent in vitro activity against cytomegalovirus, a frequent cause of disease in immunosupressed patients. Studies have been carried out to assess their efficacy in patients and their toxicity. These studies appear to be one of the few organized trials assessing this promising compound. AIDS patients with CMV retinitis, colitis, or pneumonitis have been treated. Retinitis responded dramatically as did colitis and pneumonitis. Bone marrow toxicity was noted to be severe in three patients. Clinical and virologic relapses occurred within several weeks of stopping therapy. One non-AIDS patient with CMV retinitis has been successfully treated. The significance of this study is that it is the first evidence of effective therapy for CMV disease. A randomized cross-over study to confirm these results is scheduled to begin.